Radiotelephones generally refer to communications terminals which provide a wireless communications link to one or more other communications terminals. Radiotelephones may be used in a variety of different applications, including cellular telephone, land-mobile (e.g., police and fire departments), and satellite communications systems.
Many radiotelephones, particularly handheld radiotelephones, employ retractable antennas which may be extended out of, and retracted back into, a radiotelephone housing. Typically, retractable antennas are electrically connected to a printed circuit board containing radio frequency circuitry located within a radiotelephone housing. A radiotelephone antenna is typically interconnected with the radio frequency circuitry such that impedance of the antenna and the radio frequency circuitry are substantially matched. Conventionally, an antenna and radio frequency circuitry are matched at about 50 ohms (.OMEGA.) impedance.
Unfortunately, matching impedance of a retractable antenna may be difficult because antenna impedance may be dependent on a position of an antenna with respect to both the housing of a radiotelephone and a printed circuit board containing the radio frequency circuitry. As these respective positions change when an antenna is moved between extended and retracted positions, an antenna typically exhibits at least two different impedance states, both of which should be matched to a 50 .OMEGA. impedance of a feed terminal from a printed circuit board. Accordingly, with retractable antennas, it is generally desirable to provide an impedance matching system with dual circuits that provide an acceptable impedance match between an antenna and radio frequency circuitry, both when an antenna is retracted, and when an antenna is extended.
Separate feed terminals may be used with impedance matching circuits to electrically connect a respective matching circuit to an antenna element. Unfortunately, multiple feed terminals may add to the complexity of a radiotelephone antenna design. Furthermore, multiple feed terminals may require mechanical parts, such as spring contacts, that may become unreliable over time.